The present disclosure generally relates to a method for improving the performance of communication systems, and more particularly to a method for artificially changing the quasi-static channel fading to time-varying channel fading condition by multiplying the transmitting signals with a set of time varying complex multipliers to improve the performance of the communication systems.
In communication systems, the term ‘fading’ generally refers to a degradation of the received signals over time caused by changes in the transmission medium or path. Fading generally results from the superposition of multiple copies of transmitted signals that have experienced attenuation, delay and phase shift while traveling from a source to a receiver. It may also be caused by attenuation of signals.
Multipath fading or small-scale fading is a kind of fading occurring with small movements of a mobile or obstacle. For example, cellular phones may experience momentary fading of receiving signals and the reason for the degradation of signals is the destructive interference that multiple reflected copies of the signal overlapped with itself. The way to cope with fading is to ensure that multiple versions of the same signal are transmitted, received, and coherently combined. This is usually termed diversity, and is sometimes acquired through multiple antennas.
A channel model describing the fading phenomenon is represented by an equation which describes the relationship between the receiving signal and transmitting signal. The receiving signal is the sum of transmitting signal multiplied with a set of time-dependent coefficients and time-varying random noise. The set of time-dependent coefficients is modeled as random variables.
In communication systems, the performance can be improved if a data packet experiences a time-varying nature of the radio channel. This is simply due to the fact that a radio channel with time-varying channel characteristic could have lower bit error rate than a radio channel with quasi-static channel characteristic in a long run. If the radio channel is operated in a time-varying multi-path fading environment, the channel coding schemes among other methods can improve the performance of the communication systems.
If the channel characteristic is not time-varying, such as in quasi-static fading condition, even channel coding schemes can not recover bit errors caused by the impairment of the radio environment because the data packet experiences same type of bit errors. Quasi-static fading channel model is the one in which channel coefficients in the channel model remain constant for at least one data packet interval. If a channel has channel coefficients staying the same for more than one data packet but less than a frame, it is called block fading channel.
Accordingly, it is desirable to provide methods for artificially changing the quasi-static fading channel to time-varying fading channel to improve the performance of the channel codes by artificially creating time-varying transmitting signals to provide time diversity. Furthermore, other desirable features and characteristics of the techniques described herein will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.